A tire has a complicated structure in which various materials, such as rubber, chemical fiber, and steel cord, are stacked. At a contact face (tread face) having such a complicated structure, uniformity of the tire radius has to be ensured and undulation (runout) of the contact face has to be restricted to prevent vertical vibration (radial runout) caused by a variation in tire radius.
Hence, occurrence of a runout is prevented in a manufacturing phase of a tire, and a runout of the contact face is inspected for a manufactured tire. In this inspection, a tire determined to have a large runout is removed from subjects to be shipped.
Owing to this, in a final step of tire manufacturing (inspection step after tire vulcanization), in particular, a runout at a tread face is measured and a shape defect at a sidewall face is inspected. A tread face of a tire has a tread pattern having protruding blocks forming contact faces and recessed grooves. Hence, when a runout at a tread face is measured, the heights of the protruding blocks at the contact faces have to be properly detected.
In recent years, for a technology of measuring a runout at such a tread face, there has been developed automation using an image inspection or the like with a laser distance sensor, a three-dimensional shape measurement device, or a camera.
For example, PTL 1 discloses a device for measuring the outer shape of a subject having bulges and dents at a surface. This device includes an optical displacement meter that provides scanning on a prescribed measurement portion of a subject, signal correction means for, in response to an output signal of the optical displacement meter, removing a prescribed signal pattern component from the output signal, and measurement means for measuring a prescribed shape based on a signal corrected by the signal correction means.
This shape measuring device evaluates a signal pattern component to be removed, by using a parameter based on an inclination of a signal pattern appearing in sampling data.